Magnesium-Alloy Member, Compressor for Use in Air Conditioner, and Method for Manufacturing Magnesium-Alloy Member

ABSTRACT

A magnesium alloy member capable of achieving a mechanical strength and a high-temperature fatigue strength sufficient for a compressor for in automotive air conditioners The magnesium alloy member is formed by subjecting a cast material of a magnesium alloy containing, on the basis of mass %, from 0.3% to 10% calcium (Ca), from 0.2% to 15% aluminum (Al), and from 0.05% to 1.5% manganese (Mn), and containing calcium (Ca) and aluminum (Al) at a calcium/aluminum mass ratio of from 0.6 to 1.7, with the balance being magnesium (Mg) and inevitable impurities to plastic working (extrusion processing) at from 250° C. to 500° C. This makes it possible to obtain a magnesium alloy member having a room-temperature 0.2% proof stress of 300 MPa or more and a 150° C. fatigue strength of 100 MPa or greater.

TECHNICAL FIELD

The present invention relates to a magnesium alloy member containingaluminum, calcium, and manganese; a compressor for air conditionersusing the magnesium alloy member as or for a mechanical part of thecompressor, and a method for manufacturing the magnesium alloy member.

BACKGROUND ART

Magnesium alloys having a low specific gravity may be used forautomotive parts in order to reduce the weight thereof. Magnesium alloyshave conventionally been used mainly for parts such as casings andcovers which need neither high strength nor heat resistance. However,there have recently been developed magnesium alloys having enhancedstrength or heat resistance.

For example, Patent Documents 1 to 3 disclose a magnesium alloy havingenhanced castability and heat resistance, whereas Patent Document 4discloses a magnesium alloy having enhanced high-temperature strengthand forgeability.

CITATION LIST Patent Documents

Patent Document 1: Japanese Laid-Open Patent Application Publication No.2004-232060

Patent Document 2: Japanese Laid-Open Patent Application Publication No.2007-197796

Patent Document 3: Japanese Laid-Open Patent Application Publication No.2004-162090

Patent Document 4: Japanese Laid-Open Patent Application Publication No.2000-104137

Patent Document 5: Japanese Laid-Open Patent Application Publication No.2000-109963

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Compressors for automotive air conditioners are installed in thevicinity of engines so that they are exposed to a temperature of fromabout 100° C. to 150° C. Materials for the parts of the compressorstherefore have preferably heat resistance. Moreover, mechanical partsengaged in compression work of the compressor have preferably a highfatigue strength at high temperatures.

Magnesium alloys disclosed in Patent Documents 1 to 3 are however usedfor casting and have insufficient mechanical strength. They are notsuited for use for parts of compressors or the like having preferablyhigh strength at high temperatures.

Although the magnesium alloys disclosed in Patent Documents 4 and 5 areexcellent in strength and forgeability, it is not certain that the canbe used for mechanical parts of compressors because a high-temperaturefatigue strength thereof has not yet been verified.

Moreover, when an expensive rare metal is added to a magnesium alloy,the resulting alloy has increased strength, but it raises themanufacturing cost so that it is not suited as a material for mechanicalparts of compressors.

Objects of the invention are therefore to provide a magnesium alloymember and a method for manufacturing a magnesium alloy member, eachcapable of realizing mechanical strength and high-temperature fatiguestrength facilitating application thereof to mechanical parts of acompressor for automotive air conditioners; and to provide a compressorfor air conditioners equipped with mechanical parts made of a magnesiumalloy having necessary mechanical strength and high-temperature fatiguestrength.

Means for Solving the Problems

In order to achieving the above-mentioned objects, the present inventionis characterized in a magnesium alloy cast material containing, on thebasis of mass %, from 0.3% to 10% calcium, from 0.2% to 15% aluminum,and from 0.05% to 1.5% manganese, and containing calcium and aluminum ata calcium/aluminum mass ratio of from 0.6 to 1.7, with the balance beingmagnesium and inevitable impurities is subjected to plastic working atfrom 250° C. to 500° C.

When both calcium (Ca) and aluminum (Al) are added, a Mg—Ca-basedcompound and a Mg—Al—Ca-based compound are crystallized at the grainboundaries, resulting in enhancement in mechanical strength at roomtemperature and heat resistance.

The compounds thus crystallized undergo a change, depending on a Ca/Almass ratio. In particular, when the Ca/Al mass ratio is set at from 0.6to 1.7, Mg₂Ca which is a Mg—Ca-based compound and (Mg,Al)₂Ca which is aMg—Al—Ca-based compound are crystallized simultaneously, so that such amass ratio is remarkably effective for the enhancement of mechanicalstrength and heat resistance.

On the other hand, when the Ca/Al mass ratio exceeds 1.7, only Mg₂Ca iscrystallized or in addition thereto, a slight amount of (Mg,Al)₂Ca iscrystallized, and thus, an effect for enhancing the mechanical strengthmay not be expected. When the Ca/Al mass ratio is below 0.6, β-Mg₁₇Al₁₂which is a Mg—Al-based compound is crystallized and it adversely affectsthe heat resistance.

Addition of a small amount of manganese (Mn) decreases the crystalparticle size, leading to enhancement in mechanical strength. The amountof manganese (Mn) added is preferably in a range of from 0.05% to 1.5%.When the amount is outside this range, an effect for enhancing themechanical strength may not be expected because such an amount is lesseffective for decreasing the crystal particle size.

It is possible to achieve high fatigue strength at high temperatures bysubjecting a cast material made of a magnesium alloy having theabove-mentioned composition to plastic working at from 250° C. to 500°C. The magnesium alloy member after plastic working at from 250° C. to500° C. has, as mechanical strength and high-temperature fatiguestrength which mechanical parts of a compressor for automotive airconditioners are desired to have, a 0.2% proof stress at roomtemperature of 300 MPa or greater and a 150° C. fatigue strength of 100MPa or greater.

When plastic working is conducted at below 250° C., the material is notformed and cracks appear because a sufficient strain amount is notproduced. When the temperature exceeds 500° C., on the other hand,high-temperature oxidation or partial melting occurs and an effect forenhancing the fatigue strength may not be expected.

The plastic working may be followed by solution heat treatment andartificial aging treatment. It is preferred to conduct, after theplastic working, solution heat treatment to retain the resultingmagnesium alloy member for 0.08 hour or more at a treatment temperatureof from 450° C. to 510° C. and then conduct artificial aging treatmentto retain it for 0.3 hour or more at a treatment temperature of from150° C. to 250° C.

When the solution heating is conducted at a treatment temperatureranging from 450° C. to 510° C., the grain boundaries or inside of thegrains are reinforced by fine precipitates. This suppresses localdeformation and widens a uniform deformation region, so that worksoftening at high temperatures does not occur easily, leading toenhancement in high-temperature fatigue strength.

The solution heating conducted at a treatment temperature below 450° C.makes it difficult to form a solid solution, reduces an amount ofprecipitates at the grain boundaries and in the grains, and preventsformation of an appropriate state, so that enhancement inhigh-temperature fatigue strength is not expected. When the solutionheating is conducted at a treatment temperature exceeding 510° C., onthe other hand, burning to melt a portion of the alloy occurs, leadingto the formation of pore defects.

The solution heating time below 0.08 hour may not achieve sufficientsolution heat treatment, and thus, retention time preferably exceeds0.08 hour.

Cooling employed for hardening may be conducted with warm water or witha certain additive. Various means may be employed insofar as thewell-known cooling means for hardening.

When artificial aging treatment is conducted at a temperature below 150°C., it takes longer to enhance the hardness to a proper one. Treatmenttemperatures exceeding 250° C. may deteriorate the hardness andstrength, so that the artificial aging treatment is conducted preferablyin a temperature range of from 150 to 250° C.

When the retention time for the artificial aging treatment is below 0.3hour, sufficient aging hardening is not achieved, and thus, theretention time for the artificial aging treatment is preferably 0.3 houror more.

As the plastic working, extrusion processing can be conducted. Extrusionprocessing at from 250° C. to 500° C. can enhance the fatigue strengthwhile suppressing cracks or surface oxidation.

The above-mentioned magnesium alloy members can be used as or formechanical parts of a compressor for air conditioners.

Advantageous Effect of the Invention

The present invention makes it possible to provide a magnesium alloymember capable of realizing mechanical strength and high-temperaturefatigue strength sufficient to use it as or for mechanical parts of acompressor for automotive air conditioners, more specifically, a 0.2%proof stress at room temperature of 300 MPa or greater and a 150° C.fatigue strength of 100 MPa or greater. In addition, the invention makesit possible to provide a compressor for air conditioners using such amagnesium alloy member as or for the mechanical parts of it.

According to the invention, a magnesium alloy member havingsubstantially equal mechanical strength and high-temperature fatiguestrength to those of high-strength aluminum alloy can be realized, sothat the high-strength aluminum alloy can be replaced by the magnesiumalloy member having a lower specific gravity than the high-strengthaluminum alloy, making it possible to realize a drastic weight reductionof a compressor for automotive air conditioners.

MODE FOR CARRYING OUT THE INVENTION

The embodiments of the invention will hereinafter be describedspecifically.

Table 1 includes tensile strength (MPa) at room temperature, forexample, from 10° C. to 35° C. and a 0.2% proof stress (MPa) of each ofa plurality of magnesium alloy samples varied in aluminum (Al), calcium(Ca), and manganese (Mn) contents (mass %).

With regards to “rating” in Table 1, “∘ ” means that a 0.2% proof stressis 300 MPa or greater, that is, a value which mechanical parts of acompressor for automotive air conditioners are desired to have and “x”means that a 0.2% proof stress is less than 300 MPa.

The “300 MPa”, that is, a desired value of a 0.2% proof stress is setusing, as a reference value, the 0.2% proof stress of an aluminum alloyforged material subjected to T6 treatment, that is, solution heattreatment followed by artificial aging treatment. This aluminum alloyforged material is used for mechanical parts of a compressor forautomotive air conditioners.

The samples listed in Table 1 were each obtained by preparing amagnesium alloy cast material having a content as described in thistable and then subjecting it to plastic working, more specifically, hotindirect extrusion processing. These samples had not been subjected toheat treatment (T6 treatment).

Described specifically, alloy melting was conducted in the atmosphere byusing an electric resistance furnace and a mixed gas of SF₆ and CO₂ wasused for preventing oxidation of the molten metal. After stirring,bubbling was conducted by supplying an Ar gas in order to remove anoxide formed at the time of Ca addition. The resulting mixture was thencast in a billet mold and thus, the cast material was prepared.

A hydraulic press was used for direct extrusion processing. The materialsample to be extruded was charged in a mold heated to 350° C. Afterretention for 10 minutes, extrusion processing was started while settingan extrusion ratio at 20. It is to be noted that the term “extrusionratio” means a (cross-sectional area before plasticworking)/(cross-sectional area after plastic working) ratio.

In a tensile test for evaluating tensile properties of an extrudedmaterial, a universal tester was employed. A test specimen was collectedwhile keeping the extruding direction and a load applying directionparallel to each other and a JIS14A test specimen having a diameter, ata test portion, of 4 mm and a gauge length of 20 mm was prepared.Moreover, an initial strain rate: 1×10⁻³ s⁻¹ was used as a test rate.

In the bottom line of Table 1, the tensile strength (MPa) and 0.2% proofstress (MPa) of an Al alloy forged material (A4032-T6) which is amaterial specified by JIS are described for reference. The “rating” inthis table indicates whether the Al alloy forged material (A4032-T6) hasa 0.2% proof stress of 300 MPa or greater or not.

In Table 1, the samples of Examples 1 to 11 were obtained by subjectinga cast material of a magnesium alloy containing from 0.3% to 10% calcium(Ca), from 0.2% to 15% aluminum (Al), and from 0.05% to 1.5% manganese(Mn), having a calcium (Ca)/aluminum (Al) mass ratio of from 0.6 to 1.7,with the balance being magnesium Mg and inevitable impurities to plasticworking (extrusion processing) at 350° C.

On the other hand, samples of Comparative Examples 1 to 7 were obtainedby subjecting a cast material of a magnesium alloy which did not satisfyat least one of the above-mentioned ranges of the calcium (Ca) content,the aluminum (Al) content, the manganese (Mn) content, and the calcium(Ca)/aluminum (Al) mass ratio to plastic working (extrusion processing)at 350° C.

It is to be noted that “Ca+Al” in Table 1 means a total mass % ofcalcium (Ca) and aluminum (Al).

As shown in Table 1, the samples of Examples 1 to 7 which satisfy thecalcium (Ca) content of from 0.3% to 10%, the aluminum (Al) content offrom 0.2% to 15%, the manganese (Mn) content of from 0.05% to 1.5%, andthe calcium (Ca)/aluminum (Al) mass ratio of from 0.6 to 1.7, each havea 0.2% proof stress of 300 MPa or greater, that is, the desired value,thus satisfying the mechanical strength which mechanical parts of acompressor for automotive air conditioners are desired to have. Thus, itis possible for them to be used as a mechanical part of a compressor.

On the other hand, the samples of Comparative Examples 1 and 4 having acalcium (Ca) content outside the range of from 0.3% to 10% and thesamples of Comparative Examples 2 and 3 having an aluminum (Al) contentoutside the range of from 0.2% to 15% have a 0.2% proof stress below 300MPa, that is, the desired value. Thus, it is impossible that they arenot suited for use as a mechanical part of a compressor.

Even if the calcium (Ca) content and the aluminum (Al) content arewithin the range of from 0.2% to 15%, when the calcium (Ca)/aluminum(Al) mass ratio is outside the range of from 0.6 to 1.7 as inComparative Example 5 or Comparative Example 6, a 0.2% proof stress doesnot reach the desired value, that is, 300 MPa, and such samples are notsuited for use as mechanical parts of a compressor.

Moreover, even if the calcium (Ca) content and the aluminum (Al) contentare within the range of from 0.3% to 10% and the calcium (Ca)/aluminum(Al) mass ratio is within the range of from 0.6 to 1.7, the sample ofComparative Example 7 not containing manganese is not suited for use asa mechanical part of a compressor, because the 0.2% proof stress isbelow 300 MPa and does not satisfy the desired value.

It has been found from the results of the tensile test that a magnesiumalloy preferably satisfies the following conditions, that is, a calcium(Ca) content of from 0.3% to 10%, an aluminum (Al) content of from 0.2%to 15%, a manganese (Mn) content of from 0.05% to 1.5%, and a calcium(Ca)/aluminum (Al) mass ratio of from 0.6 to 1.7 in order to achieve themechanical strength necessary for mechanical parts of a compressor forautomotive air conditioners, more specifically, to achieve a 0.2% proofstress of 300 MPa or greater.

By the addition of both calcium (Ca) and aluminum (Al), a Mg—Ca-basedcompound and a Mg—Al—Ca-based compound are crystallized at the grainboundaries, leading to enhancement in mechanical strength at roomtemperature and heat resistance. When the calcium (Ca)/aluminum (Al)mass ratio is adjusted to from 0.6 to 1.7 as in Examples 1 to 11, Mg₂Cawhich is a Mg—Ca-based compound and (Mg,Al)₂Ca which is anMg—Al—Ca-based compound are crystallized simultaneously, which ispresumed to lead to enhancement in mechanical strength and heatresistance.

When the calcium (Ca)/aluminum (Al) mass ratio exceeds 1.7 as inComparative Example 6, only Mg₂Ca is crystallized or in additionthereto, a slight amount of (Mg,Al)₂Ca is crystallized, which does notlead to sufficient enhancement in mechanical strength. When the calcium(Ca)/aluminum (Al) mass ratio falls below 0.6 as in Comparative Example5, β-Mg₁₇Al₁₂ which is a Mg—Al-based compound is crystallized, which ispresumed to adversely affect the heat resistance.

Even when the calcium (Ca)/aluminum (Al) mass ratio falls within therange of from 0.6 to 1.7, in a case in which magnesium (Mn) is not addedas in Comparative Example 7, sufficient mechanical strength may not beachieved. On the other hand, by the addition of a small amount ofmanganese (Mn) as in Examples 1 to 11, a 0.2% proof stress of 300 MPa orgreater can be achieved, which is presumed to occur because the crystalparticle size becomes finer and mechanical strength is enhanced by theaddition of a small amount of manganese (Mn). The amount of manganese(Mn) is appropriately in a range of from 0.05% to 1.5%. Amounts outsidethis range are less effective for reducing the particle size of crystalsand an effect of enhancing the mechanical strength may not be expected.

TABLE 1 Tensile 0.2% proof Ca Al Mn Ca/Al Ca + Al strength stress [wt %][wt %] [wt %] [—] [wt %] [MPa] [MPa] Rating Example 1 0.34 0.54 0.290.63 0.88 328 312 ∘ Example 2 1.5 2.4 0.23 0.63 3.9 350 335 ∘ Example 33.3 3.7 0.33 0.89 7 349 330 ∘ Example 4 3 5 0.31 0.60 8 340 330 ∘Example 5 5.8 8.1 0.36 0.72 13.9 339 321 ∘ Example 6 7.6 6.8 0.39 1.1214.4 327 319 ∘ Example 7 9.4 8.2 0.43 1.15 17.6 321 310 ∘ Example 8 9.25.8 0.24 1.59 15 322 309 ∘ Example 9 3.8 14.5 0.37 0.26 18.3 318 304 ∘Example 3.7 3.9 0.06 0.95 7.6 329 318 ∘ 10 Example 0.33 0.23 0.26 1.430.56 321 304 ∘ 11 Comp. 0.23 0.3 0.21 0.77 0.53 320 288 x Ex. 1 Comp.0.31 0.19 0.18 1.63 0.5 313 285 x Ex. 2 Comp. 9.7 15.4 0.33 0.63 25.1326 297 x Ex. 3 Comp. 11.6 14.2 0.24 0.82 25.8 263 231 x Ex. 4 Comp. 3.36.8 0.25 0.49 10.1 298 272 x Ex. 5 Comp. 6.1 3.4 0.21 1.79 9.5 311 289 xEx. 6 Comp. 3.2 3.7 0 0.86 6.9 304 278 x Ex. 7 A4032- — 350 300 — T6

The samples listed in Table 2 are the cast materials of a magnesiumalloy of Example 3 having the contents indicated in Table 1, that is, acalcium (Ca) content of 3.3%, an aluminum (Al) content of 3.7%, and amanganese (Mn) content of 0.33%, a calcium (Ca)/aluminum (Al) mass ratioof 0.89, and a total content of calcium (Ca) and aluminum (Al) of 7%.These cast materials were subjected to extrusion processing (plasticworking) at varied extrusion ratios and extrusion temperatures and theresults of a 0.2% proof stress test of the samples obtained by extrusionprocessing are listed.

In the tests of Table 2, the extrusion ratio was set at four ratios,that is, 10, 20, 40, and 60. When the extrusion temperature at each ofthese extrusion ratios was in a range of from 250° C. to 500° C.,neither cracks nor surface oxidation occurred and the 0.2% proof stressexceeded the desired value, that is, 300 MPa.

On the other hand, when the extrusion ratio was set at 20 and theextrusion temperature was set at 230° C., which was a temperature belowthe range of from 250° C. to 500° C., cracks occurred and desiredmechanical strength was not attained. When the extrusion temperature wasset at 517° C., which was a temperature exceeding the range of from 250°C. to 500° C., surface oxidation occurred and the 0.2% proof stress wasbelow the desired value, that is, 300 MPa.

It has been found that by controlling the temperature of the plasticworking (extrusion processing) to fall within a range of from 250° C. to500° C., the 0.2% proof stress of 300 MPa or more can be attained.Plastic working results in failure and cracks appear at a plasticworking temperature below 250° C., because a sufficient strain amountcannot be secured. At the plastic working temperature exceeding 500° C.,high-temperature oxidation or partial melting occurs and thereforeenhancement in fatigue strength may not be expected.

TABLE 2 0.2% Proof Extrusion Temperature stress Component ratio [—] [°C.] [MPa] Rating Remarks Example 3 10 350 311 ∘ 20 350 330 ∘ 20 230 — xCracks 20 470 308 ∘ 20 517 278 x Surface oxidation 20 280 303 ∘ 50 350334 ∘ 60 400 339 ∘ 60 300 342 ∘

Table 3 includes measurement results of a 150° C. fatigue strength(high-temperature fatigue strength) of a sample subjected to plasticworking (extrusion processing) at from 250° C. to 500° C., followed byheat treatment (T6 treatment) and a sample not subjected to heattreatment (T6 treatment) after the plastic working.

It is to be noted that as a sample, used was that obtained by subjectingthe cast material of a magnesium alloy of Example 3 having the contentsindicated in Table 1, that is, a calcium (Ca) content of 3.3%, analuminum (Al) content of 3.7%, a manganese (Mn) content of 0.33%, acalcium (Ca)/aluminum (Al) mass ratio of 0.89, and a total content ofcalcium (Ca) and aluminum (Al) of 7% to extrusion processing at anextrusion ratio of 20 and an extrusion temperature of 350° C.

In Table 3, the 150° C. fatigue strength of an Al alloy forged material(A4032-T6) which is a material specified by JIS is also listed forcomparison in Table 3. As describe above, this Al alloy forged material(A4032-T6) has been used for a compressor for automotive airconditioners, and thus, a material capable of achieving a 150° C.fatigue strength at least equal to the 150° C. fatigue strength of thisA4032-T6 (100 MPa) can be used as a substitute member of A4032-T6.

The fatigue test (rotary bending test) for finding the fatigue strengthof Table 3 and calculation of a fatigue strength were conducted inaccordance with “The Japan Society of Mechanical Engineers, Standardmethod of statistical fatigue testing (revised) JSME S-002-1994” ed. byThe Japan Society of Mechanical Engineers. The test was conducted at atest temperature of 150° C., a rotating speed of 3000 rpm, a frequencyof 50 Hz, and a stress ratio R of −1. The fatigue strength in Table 3 isthe result of the tests conducted 10⁷ times.

The test specimen used for the fatigue test is a rod-type test specimen.The diameter at a chuck portion was 8.5 mm and the diameter at abreaking portion was 4 mm. It was collected so that the extrudingdirection and the load applying direction were orthogonal to each other.In order to remove the influence of streaks due to cutting, the breakingportion was polished with waterproof abrasive paper, followed by buffingto finish.

In addition, as the T6 treatment, solution heat treatment to retain thesample in an Ar gas stream of 500° C. for 30 minutes (0.5 hour) wasconducted in a horizontal tubular furnace and then, artificial agingtreatment was conducted in an oil bath of 180° C. for 2 hours. The heattreatment time (retention time) is a period of time starting with thecharging of the sample.

As listed in Table 3, the 150° C. fatigue strength of A4032-T6 is 100MPa; the 150° C. fatigue strength of the magnesium alloy membersubjected to plastic working at a temperature of from 250° C. to 500°C., more specifically, subjected to extrusion processing at 350° C. andnot subjected to the heat treatment (T6 treatment) thereafter was 117MPa; and the 150° C. fatigue strength of the magnesium alloy memberhaving the same composition, subjected to the same plastic working, andthen subjected to the heat treatment (T6 treatment) was 132 MPa.

This means that the 150° C. fatigue strength exceeding that of A4032-T6can be achieved by subjecting the magnesium alloy cast material having acalcium (Ca) content of from 0.3% to 10%, an aluminum (Al) content offrom 0.2% to 15%, a manganese (Mn) content of from 0.05% to 1.5%, and acalcium (Ca)/aluminum (Al) mass ratio of from 0.6 to 1.7 to plasticworking at from 250 to 500° C. even without subjecting it to heattreatment (T6 treatment). The material subjected to the heat treatment(T6 treatment) in addition to the plastic working has an enhanced 150°C. fatigue strength compared with the material not subjected to the heattreatment (T6 treatment).

In other words, a magnesium alloy member obtained by subjecting themagnesium alloy cast material having a calcium (Ca) content of from 0.3%to 10%, an aluminum (Al) content of from 0.2% to 15%, a manganese (Mn)content of from 0.05% to 1.5%, and a calcium (Ca)/aluminum (Al) massratio of from 0.6% to 1.7 to plastic working at from 250° C. to 500° C.can achieve a room-temperature 0.2% proof stress and a high-temperaturefatigue strength suited for use for mechanical parts of a compressor forautomotive air conditioners, more specifically, the room-temperature0.2% proof stress of 300 MPa or greater and 150° C. fatigue strength of100 MPa even without the heat treatment (T6 treatment). The membersubjected to the heat treatment (T6 treatment) in addition to theplastic working has a further enhanced high-temperature fatiguestrength.

It is therefore possible to use a magnesium alloy member instead of aconventionally used high-strength aluminum alloy for the formation ofmechanical parts of a compressor for automotive air conditioners. Thismakes it possible to realize a remarkable reduction in the weight of thecompressor.

TABLE 3 150° C. Rotary bending fatigue strength Component, T6 treatment[MPa] Example 3, subjected to T6 132 treatment Example 3, not subjectedto T6 117 treatment A4032 forged product, subjected to 100 T6 treatment

It is to be noted that in the heat treatment (T6 treatment), it ispreferred that the solution heat treatment after plastic working(extrusion processing) be conducted while retaining the magnesium alloymember for 0.08 hour or more at a treatment temperature of from 450° C.to 510° C. and the artificial aging treatment after hardening treatmentis conducted while retaining the member for 0.3 hour or more at atreatment temperature of from 150° C. to 250° C.

At treatment temperatures of solution heat treatment within a range offrom 450° C. to 510° C., the grain boundaries and the inside of thegrains are reinforced with fine precipitates, local deformation issuppressed, and a uniform deformation area is widened, so that worksoftening at high temperatures is suppressed and the resulting alloymember has an enhanced high-temperature fatigue strength.

The solution heating conducted at a treatment temperature below 450° C.makes it difficult to form a solid solution, reduces an amount ofprecipitates at the grain boundaries and in the grains, and preventsformation of an appropriate state, so that enhancement inhigh-temperature fatigue strength is not expected. When the solutionheating is conducted at a treatment temperature exceeding 510° C., onthe other hand, burning to melt a portion of the alloy occurs, leadingto the formation of pore defects.

The solution heating time below 0.08 hour may not achieve sufficientsolution heat treatment, and thus, retention time is preferably greaterthan 0.08 hour.

Treatment temperatures of the artificial aging treatment below 150° C.may increase the treatment time in order to attain a proper hardness,whereas treatment temperatures exceeding 250° C. deteriorate thehardness and strength. The temperature of the artificial aging treatmentis preferably in a range of from 150° C. to 250° C.

Retention time of the artificial aging treatment below 0.3 hour cannotachieve sufficient aging hardening, and thus, the retention time of theartificial aging treatment is preferably 0.3 hour or greater.

The temperature and retention time of the heat treatment (T6 treatment)which have provided the results of Table 3 satisfy the above-mentionedtemperature range and time range.

As described above, the magnesium alloy member and the method formanufacturing the magnesium alloy member according to the invention canrealize a room-temperature 0.2% proof stress of 300 MPa or greater and a150° C. fatigue strength of 100 MPa or greater which are necessary formechanical parts of a compressor for automotive air conditioners andtherefore the magnesium alloy member of the invention can be usedinstead of the conventionally used Al alloy forged material A4032.

Since the magnesium alloy member has a lower specific gravity than theAl alloy forged material A4032, when mechanical parts of a compressorfor automotive air conditioners are made of the magnesium alloy, it ispossible to markedly reduce the weight of the compressor, reduce theweight of the automotive, and therefore enhance the fuel efficiency.

Examples of the magnesium alloy member of the invention and mechanicalparts of a compressor for automotive air conditioners to which themagnesium alloy member is applied include shoes and pistons for swashplate compressors and spiral bodies for scroll type compressors.

The magnesium alloy member and the method for manufacturing a magnesiumalloy member according to the invention have been developed with a viewto applying them to mechanical parts of a compressor for automotive airconditioners, but they can be applied not only to the mechanical partsof a compressor for automotive air conditioners but also to mechanicalparts of a compressor for stationary air conditioners.

In addition, the plastic working is not limited to extrusion processingand it may be forging, rolling, or drawing processing.

1. A magnesium alloy member obtained by subjecting a cast material of amagnesium alloy containing, on the basis of mass %, from 0.3% to 10%calcium, from 0.2% to 15% aluminum, and from 0.05% to 1.5% manganese,and containing calcium and aluminum at a calcium/aluminum mass ratio offrom 0.6 to 1.7, with the balance being magnesium and inevitableimpurities to plastic working at from 250° C. to 500° C.
 2. Themagnesium alloy member according to claim 1, wherein the plastic workingis followed by solution heat treatment and artificial aging treatment.3. The magnesium alloy member according to claim 2, wherein after theplastic working, the magnesium alloy member is subjected to solutionheat treatment to retain the magnesium alloy member for at least 0.08hour at a treatment temperature of from 450° C. to 510° C., and then,the resulting member is subjected to artificial aging treatment toretain the resulting member for at least 0.3 hour at a treatmenttemperature of from 150° C. to 250° C.
 4. A magnesium alloy memberobtained by subjecting a cast material of a magnesium alloy containing,on the basis of mass %, from 0.3% to 10% calcium, from 0.2% to 15%aluminum, and from 0.05% to 1.5% manganese, and containing calcium andaluminum at a calcium/aluminum mass ratio of from 0.6 to 1.7, with thebalance being magnesium and inevitable impurities to plastic working;and having a room-temperature 0.2% proof stress of 300 MPa or greaterand a 150° C. fatigue strength of 100 MPa or greater.
 5. The magnesiumalloy member according to claim 1, wherein the plastic working isextrusion processing.
 6. A compressor for air conditioners using, as amechanical part thereof, the magnesium alloy member as claimed inclaim
 1. 7. A method for manufacturing a magnesium alloy member,comprising subjecting a cast material of a magnesium alloy containing,on the basis of mass %, from 0.3% to 10% calcium, from 0.2% to 15%aluminum, and from 0.05% to 1.5% manganese, and containing calcium andaluminum at a calcium/aluminum mass ratio of from 0.6 to 1.7, with thebalance being magnesium and inevitable impurities to plastic working atfrom 250° C. to 500° C.
 8. The method for manufacturing a magnesiumalloy member according to claim 7, wherein the plastic working isfollowed by solution heat treatment and artificial aging treatment. 9.The method for manufacturing a magnesium alloy member according to claim8, further comprising, after the plastic working, subjecting themagnesium alloy member to solution heat treatment to retain the memberfor at least 0.08 hour at a treatment temperature of from 450° C. to510° C., and then, subjecting the resulting member to artificial agingtreatment to retain the resulting member for at least 0.3 hour at atreatment temperature of from 150° C. to 250° C.
 10. The method formanufacturing a magnesium alloy member according to claim 7, wherein theplastic working is extrusion processing.